Crosslinked fluoropolymer networks

ABSTRACT

Disclosed herein is a crosslinked fluoropolymer network formed by the free radical initiated crosslinking of a diacrylate fluoropolymer The diacrylate copolymer is of formula CH2═CR′COO—(CH2)n—R—(CH2)n—OOCR′═CH2, wherein R is selected from the group consisting of i) an oligomer comprising copolymerized units of vinylidene fluoride and perfluoro(methyl vinyl ether), ii) an oligomer comprising copolymerized units of vinylidene fluoride and hexafluoropropylene, iii) an oligomer comprising copolymerized units of tetrafluoroethylene and perfluoro(methyl vinyl ether), and iv) an oligomer comprising copolymerized units of tetrafluoroethylene and a hydrocarbon olefin, R′ is H or —CH3, n is 1-4 and wherein said oligomer has a number average molecular weight of 1000 to 25,000 daltons. The source of the free radicals may be a photoinitiator or an organic peroxide.

FIELD OF THE INVENTION

This invention relates to crosslinked fluoropolymer networks formed bythe free radical initiated reaction of fluoropolymers having acrylategroups at both ends of main polymer chains.

BACKGROUND OF THE INVENTION

Elastomeric fluoropolymers (i.e. fluoroelastomers) exhibit excellentresistance to the effects of heat, weather, oil, solvents and chemicals.Such materials are commercially available and are most commonly eithercopolymers of vinylidene fluoride (VF₂) with hexafluoropropylene (HFP)or copolymers of VF₂, HFP, and tetrafluoroethylene (TFE).

Other common fluoroelastomers include the copolymers of TFE with one ormore hydrocarbon olefins such as ethylene (E) or propylene (P), and alsothe copolymers of TFE with a perfluoro(alkyl vinyl ether) such asperfluoro(methyl vinyl ether) (PMVE).

Many fluoroelastomers require incorporation of a cure site monomer intotheir polymer chains in order to crosslink efficiently (Logothetis, A.L., Prog. Polym. Sci., Vol. 14, pp 251-296 (1989); A. Taguet et al.Advances in Polymer Science, Vol. 184, pp 127-211 (2005)). Without sucha cure site monomer, the fluoroelastomer may not react at all withcuring agents, it may only partially react, or reaction may be too slowfor use on a commercial scale. Seals made from poorly crosslinkedelastomers often fail sooner than might otherwise be expected.Unfortunately, disadvantages are associated with many of the cure sitemonomers and curatives in use today. For example, some curatives (e.g.diamines) are toxic. Cure site monomers which contain reactive bromineor iodine atoms can release byproducts during the curing reaction thatare harmful to the environment. Other cure site monomers (e.g. thosewhich contain double bonds at both ends of the molecule) may be soreactive that they disrupt polymerization of the fluoroelastomer byaltering the polymerization rate, terminating polymerization, or bycausing undesirable chain branching, or even gelation to occur. Lastly,incorporation of a cure site monomer into a fluoroelastomer polymerchain may negatively impact the properties of the fluoroelastomer (bothphysical properties and chemical resistance).

There exists a need in the art for new fluoroelastomer cure systemswhich are environmentally friendly, do not disrupt polymerization andwhich do not detract from the properties of the fluoroelastomer.

Telechelic difunctional low molecular weight (number average molecularweight between 1000 and 25,000 daltons) copolymers of vinylidenefluoride (VF₂) with perfluoro(methyl vinyl ether) (PMVE) anddifunctional copolymers of tetrafluoroethylene (TFE) with PMVE have beendisclosed in US 20090105435 A1. A functional group is located at eachend of the copolymer main chain. Functional groups disclosed includeiodine, allyl, hydroxyl, carboxyl and nitrile.

SUMMARY OF THE INVENTION

The present invention is a crosslinked fluoropolymer network formed bythe free radical initiated reaction of a fluoropolymer having anacrylate group on each end of its main polymer chain.

Accordingly an aspect of the present invention is a process for themanufacture of a crosslinked fluoropolymer network, said processcomprising:

A) providing a telechelic diacrylate copolymer of formulaCH₂═CR′COO—(CH₂)_(n)—R—(CH₂)_(n)—OOCCR′═CH₂, wherein R′ is H or —CH₃, nis 1-4 and R is an oligomer having a number average molecular weight of1000 to 25,000 daltons, said oligomer selected from the group consistingof i) an oligomer comprising copolymerized units of vinylidene fluorideand perfluoro(methyl vinyl ether), ii) an oligomer comprisingcopolymerized units of vinylidene fluoride and hexafluoropropylene, iii)an oligomer comprising copolymerized units of tetrafluoroethylene andperfluoro(methyl vinyl ether), and iv) an oligomer comprisingcopolymerized units of tetrafluoroethylene and a hydrocarbon olefin;

B) mixing said diacrylate copolymer with a source of free radicalsselected from the group consisting of photoinitiators and organicperoxides to form a curable composition; and

C) generating free radicals to form a crosslinked fluoropolymer network.

Another aspect of the invention is a crosslinked fluoropolymer networkmade by the process comprising:

A) providing a diacrylate copolymer of formulaCH₂═CR′COO—(CH₂)_(n)—R—(CH₂)_(n)—OOCCR′═CH₂, wherein R′ is H or —CH₃, nis 1-4 and R is an oligomer having a number average molecular weight of1000 to 25,000 daltons, said oligomer selected from the group consistingof i) an oligomer comprising copolymerized units of vinylidene fluorideand perfluoro(methyl vinyl ether), ii) an oligomer comprisingcopolymerized units of vinylidene fluoride and hexafluoropropylene, iii)an oligomer comprising copolymerized units of tetrafluoroethylene andperfluoro(methyl vinyl ether), and iv) an oligomer comprisingcopolymerized units of tetrafluoroethylene and a hydrocarbon olefin;

B) mixing said diacrylate copolymer with a source of free radicalsselected from the group consisting of photoinitiators and organicperoxides to form a curable composition; and

C) generating free radicals to form a crosslinked fluoropolymer network.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to crosslinked fluoropolymer networksand to a process for the manufacture of said networks.

Fluoropolymers employed to make the crosslinked networks of theinvention have an acrylate or methacrylate group at each end of polymermain chains. By “main chain” is meant the longest chain of copolymerizedmonomer units, i.e. not side chains or branches.

The telechelic diacrylate fluoropolymers employed in this invention havethe formula CH₂═CR′COO—(CH₂)_(n)—R—(CH₂)_(n)—OOCCR′═CH₂, wherein R′ is Hor —CH₃, n is 1-4 (preferably 2 or 3) and R is an oligomer having anumber average molecular weight of 1000 to 25,000 daltons, preferably1200 to 12,000 daltons, most preferably 1500 to 5000 daltons. Oligomer,R, is selected from the group consisting of i) an oligomer comprisingcopolymerized units of vinylidene fluoride and perfluoro(methyl vinylether), ii) an oligomer comprising copolymerized units of vinylidenefluoride and hexafluoropropylene, iii) an oligomer comprisingcopolymerized units of tetrafluoroethylene and perfluoro(methyl vinylether), and iv) an oligomer comprising copolymerized units oftetrafluoroethylene and a hydrocarbon olefin. Hydrocarbon olefinsinclude ethylene (E) and propylene (P). Optionally, oligomer, R, mayfurther comprise at least one additional comonomer, different from theother two comonomers. Examples of such additional comonomers include,but are not limited to vinylidene fluoride (VF₂), hexafluoropropylene(HFP), tetrafluoroethylene (TFE) and perfluoro(methyl vinyl ether)(PMVE).

Specific examples of oligomers that may be employed in thefluoropolymers (and the diols used to make them) include, but are notlimited to TFE/PMVE, VF₂/PMVE, VF₂/TFE/PMVE, TFE/PMVE/E, VF₂/HFP,VF₂/HFP/TFE, TFE/P and TFE/P/VF₂.

The telechelic diacrylate fluoropolymers employed in this invention maybe made by a process comprising A) providing a diol of formulaHO—(CH₂)_(n)—R—(CH₂)_(n)—OH, wherein n and R are defined above; and B)reacting said diol with an acryloyl halide or methacryloyl halide (e.g.acryloyl chloride or methacryloyl chloride) to form a diacrylatecopolymer of formula CH₂═CR′COO—(CH₂)_(n)—R—(CH₂)_(n)—OOCCR′═CH₂,wherein R′ is H (if an acryloyl halide is employed) or —CH₃ (if amethacryloyl halide is employed).

Diols of formula HO—(CH₂)_(n)—R—(CH₂)_(n)—OH may be made from amulti-step process beginning with the corresponding α,ω-diiodo oligomersof formula I—R—I prepared generally as described in U.S. 20090105435 A1.

The telechelic diiodo oligomers may be ethylenated (or allylated) byreaction, in the presence of a radical initiator, with ethylene (orallyl alcohol, followed by the selective reduction of the iodine atoms).The resulting oligomers may then be hydrolyzed to form the diols.

The crosslinked fluoropolymer networks of this invention are made byexposing the diacrylate fluoropolymer to a source of free radicals inorder to initiate a radical crosslinking reaction through the terminalacrylate groups on the fluoropolymer. The source of the free radicalsmay be a UV light sensitive radical initiator (i.e. a photoinitiator orUV initiator) or the thermal decomposition of an organic peroxide.Suitable photoinitiators and organic peroxides are well known in thefluoroelastomers art.

Specific examples of photoinitiators include, but are not limited toDarocur® photoinitiator 1173, Irgacure® curative 819 and Irgacure®curative 907 (available from Ciba Specialty Chemicals).

A specific example of an organic peroxide includes, but is not limitedto t-butylperoxypivalate.

Optionally, a composition containing diacrylate fluoropolymer and freeradical source may be shaped prior to generating free radicals.

Compositions containing the diacrylate fluoropolymer and free radicalsource may be made by combining the fluoropolymer and radical source inconventional rubber industry mixers such as 2-roll mills and internalmixers. Optionally other ingredients such as fillers (e.g. carbon black,mineral fillers, fluoropolymer micropowders, etc.), colorants, processaids, etc. commonly employed in the rubber industry may be included inthe compositions.

Crosslinking takes place by exposing the fluoropolymer composition to UVradiation (if a photoinitiator is employed) or to sufficient heat todecompose the peroxide (if an organic peroxide is employed). Optionally,the fluoropolymer composition may contain both a photoinitiator and anorganic peroxide, so that both UV radiation and heat are employed tocrosslink the fluoropolymer.

The crosslinked fluoropolymer networks of this invention are useful asdurable coatings and films having good flexibility, chemical resistanceand thermal properties.

EXAMPLES Test Methods

Number average molecular weight (Mn) of non-crosslinked telechelicfluoropolymers was determined by size exclusion chromatography (SEC).Samples were dissolved in THF. Analyses were performed with aSpectra-Physics chromatograph equipped with two PLgel 5 μm Mixed-Ccolumns from Polymer Laboratories and a Spectra Physics SP8430Refractive Index (RI) and UV detector. Tetrahydrofuran (THF) was used aseluent, with a flow rate of 0.8 mL min⁻¹. Standards were monodispersedpoly(styrene) (PS) or poly(methylmethacrylate), purchased from PolymerLaboratories or other vendors.

Fluoropolymer and oligomer compositions and microstructures weredetermined by ¹⁹F and ¹H NMR spectroscopy. NMR spectra were recorded ona Bruker AC 400 (400 MHz) instrument, using deuterated acetone assolvent and tetramethylsilane (TMS) (or CFCl₃) as the references for ¹H(or ¹⁹F) nuclei. Coupling constants and chemical shifts are given in Hzand ppm, respectively. The experimental conditions for ¹H (or ¹⁹F) NMRspectra were the following: flip angle 90° (or 30°), acquisition time4.5 s (or 0.7 s), pulse delay 2 s (or 5 s), number of scans 16 (or 64),and a pulse width of 5 μs for ¹⁹F NMR.

The telechelic diacrylate fluoropolymers employed in the examples weremade by the following procedures.

FP1, CH₂═CHCOO—(CH₂)₂—R—(CH₂)₂—OOCCH═CH₂, wherein R is poly(vinylidenefluoride-co-perfluoro(methyl vinyl ether) [i.e. poly(VF₂-co-PMVE)].

The diol oligomer employed in the fluoropolymer manufacturing processwas made from a multi-step process, beginning with a telechelic diiodooligomer of formula I-(VF₂-co-PMVE)-I. The latter was made by theprocess disclosed in U.S. 20090105435 A1. This diiodo oligomer contained71.5 mol % VF₂ and 28.5 mol % PMVE and had a number average molecularweight of 2500 daltons.

Ethylenation of the Diiodo Oligomer:

A 160 mL Hastelloy (HC-276) autoclave, equipped with inlet and outletvalves, a manometer and a rupture disc, was degassed and pressurizedwith 30 bar of nitrogen to check for leaks. Then, a 0.5 mm Hg vacuum wasoperated for 5 minutes (min.) and subsequently an argon atmosphere wasapplied. Such a procedure of autoclave degassing was repeated fivetimes. Under vacuum, 5.0 g (2.87×10⁻² mole) of t-butylperoxypivalate(TBPPi), 50 mL of t-butanol and 100.0 g (0.077 mole) of theabove-described telechelic diiodo oligomer were transferred into theautoclave. 6.0 g of ethylene (0.214 mole) was introduced into theautoclave. Then, the autoclave was progressively heated to 75° C. Anexotherm was observed of about 10° C. and an increase of pressure from15 bars up to 18 bars, followed by a drop of pressure to 14 bars over 16hours. After reaction, the autoclave was placed in an ice bath for about60 minutes and 0.5 g of unreacted ethylene was slowly released. Afteropening the autoclave, the reaction mixture was dissolved in 100 ml ofbutanone and washed with distilled water (2×100 ml), Na₂S₂O₅ solution(100 ml) and brine (100 ml) respectively in a separating funnel. Then,the organic phase was dried over MgSO₄ and filtered through sinteredglass (G4). The organic solvent was removed by a rotary vacuumevaporator at 40° C., reducing pressure to 10 mm Hg. The resultingslightly yellow viscous liquid was dried at 40° C. under 0.01 mbarvacuum to constant weight. The yield of the reaction was 91%. Theproduct was analyzed by ¹H NMR and ¹⁹F NMR spectroscopy. An absence ofthe signal corresponding to the terminal —CF₂I (approximately −39 ppm)indicated quantitative conversion of the telechelicdiiodopoly(VF₂-co-PMVE) to ethylenated oligomer.

Hydrolysis of Ethylenated Copolymer:

To a 250 ml two-neck round-bottom flask equipped with a reflux condenserand magnetic stirrer was introduced 61.6 g (0.044 mole) of ethylenatedproduct synthesized above and 80.4 g (1.1 moles) of DMF. Then, themixture was purged with nitrogen for 20 min. and 4.0 g of water wasadded through a septum. The reaction was heated up to 120° C. andstirred overnight. After 14 hours, the crude product (reaction mixture)was cooled to room temperature and a mixture of H₂SO₄ (25 g) in methanol(70 g) was added dropwise. The reaction was kept at room temperature for24 hrs. Then, the reaction mixture was washed with distilled water(3×100 ml) and ethyl acetate (200 ml) in a separating funnel. Theorganic phase was dried over MgSO₄ and filtered through sintered glass(G4). The ethyl acetate and traces of DMF were removed by a rotaryvacuum evaporator (40° C./20 mm Hg). The resulting brown viscous liquidwas dried at 40° C. and 0.01 mbar to constant weight. The product (yield74 wt %) was analyzed by ¹H NMR, ¹⁹F NMR spectroscopy.

Conversion to Acrylates:

A 250 ml two-neck round-bottom flask equipped with a reflux condenserand magnetic stirrer was charged with 25.0 g (19.2 mmoles) of diolsynthesized above dissolved in 100 ml of THF (dried), and 12 g ofpoly(vinylpyridine). The reaction mixture was cooled to 0° C. undernitrogen atmosphere and 20 mg (0.18 mmoles) of hydroquinone were added.Acryloyl chloride was added by syringe through a septum in foursubsequent doses (4 g, 4 g, 2 g, 4 g, respectively) in the interval of 6hours (hrs). An additional 10 g of poly(vinylpyridine) was added to thereaction mixture. After addition of the first dose of acryloyl chloride,the reaction temperature was kept at 40° C. over a period of 48 hrs.Poly(vinylpyridine) was removed by filtration through sintered glass G4.Then a butanone/water (1/1) mixture was added and subsequently washedwith water. The organic layer was dried over MgSO₄ and then filteredthrough sintered glass (G4). The solvents and excess acryloyl chloridewere removed using a rotary vacuum evaporator (40° C./20 mm Hg). Theresulting brown viscous liquid was dried at 40° C. under 0.01 mbarvacuum to constant weight. The product (yield 81%) was analyzed by ¹Hand ¹⁹F NMR.

FP2, CH₂═CHCOO—(CH₂)₃—R—(CH₂)₃—OOCH═CH₂, wherein R is poly(vinylidenefluoride-co-perfluoro(methyl vinyl ether) [i.e.poly(VF₂-co-PMVE)copolymer].

Conversion to Telechelic Bis-Iodohydrin:

A 100 ml two-neck round-bottom flask equipped with a reflux condenserand a magnetic stirrer was charged with 10.5 g (6 mmoles) of theabove-described telechelic I-(VF₂-co-PMVE)-I, 2.05 g (34.4 mmoles) ofallyl alcohol and 50 ml of CH₃CN. Then the flask was heated to 80° C.AlBN (2,2′azobisisobutyronitrile) was added in 10 doses (20 mg each)with the addition interval of 30 min. The reaction was conducted undernitrogen atmosphere at 80° C. for 21 hours. After cooling to roomtemperature (about 25° C.), the reaction mixture was filtered throughcotton and then the solvent and excess allyl alcohol were removed on arotary vacuum evaporator (40° C./20 mm Hg). The resulting slightlyyellow viscous liquid was dried (40° C./0.01 mbar) to constant weight.The product (yield 93%) was analyzed by ¹H and ¹⁹F NMR, and FT-IRspectroscopy.

Reduction of Fluorinated Telechelic Di-Iodohydrin to Bis(PropylAlcohol):

A 250 ml three-neck round bottom flask equipped with a reflux condenserand a magnetic stirrer was charged with 11.5 g (6.6 mmoles) of theabove-prepared telechelic bis-iodohydrin, 4.8 g (16.5 mmoles) of Bu₃SnHand 50 ml of CH₃CN. Then the flask was heated to 70° C. AlBN(2,2′-azobisisobutyronitrile) was added in 10 doses (55 mg each) with aninterval of 60 min. between additions. The reaction was conducted undernitrogen atmosphere at 70° C. for 12 hours. After cooling to roomtemperature, 0.6 g of KF was added together with 50 ml of Et₂O. Then thereaction was stirred at about 25° C. for 24 hours. The reaction mixturewas filtered through sintered glass (G5) to remove white solid such asBu₃SnK, Bu₃SnF or Bu₃SnI. The solvents were removed on a rotary vacuumevaporator (40° C./20 mm Hg). The crude product was dissolved in 50 mlof butanone and washed with water (2×50 ml). The organic layer was driedover MgSO₄ which was then filtered through sintered glass (G4). Thebutanone was partly removed on a rotary vacuum evaporator and residuewas precipitated from pentane. After cooling 12 hours at 4° C., pentanewas carefully removed from the precipitated product by decantation. Theresidual solvent was removed by rotary vacuum evaporation (40° C./20 mmHg). The resulting light yellow viscous liquid was dried (40° C./0.01mbar) to constant weight. The product (overall yield 91%) was analyzedby ¹H and ¹⁹F NMR and FT-IR spectroscopy. The decanted pentane was alsoevaporated to give a low molecular weight fraction of the desiredpolymer.

Acrylation of Diol:

A 100 ml three-neck round bottom flask equipped with a reflux condenserand a magnetic stirrer was charged with 5.03 g (3.33 mmoles) of theabove-prepared telechelic bis(propyl alcohol)-poly(VF₂-co-PMVE), 25 mlof THF, 4.5 g of poly(vinylpolypyrolidone), 5 mg (0.045 mmoles) ofhydroquinone and cooled to 0° C. Then acryloyl chloride (4.456 g, 4 ml,50 mmoles) was added dropwise in three doses (2 ml, 1 ml & 1 ml). Afterthe first addition of acryloyl chloride, the reaction temperature wasincreased to 40° C.; the two subsequent additions were completed afterelapsed times of 5 and 22 hours. An additional amount ofpoly(vinylpolypyrolidone) (4.5 g) was then added to the reactionmixture. The reaction was conducted under nitrogen atmosphere at 40° C.for 48 hours. After cooling to room temperature, the reaction mixturewas filtered through sintered glass (G4) to removepoly(vinylpolypyrolidone). The filtered poly(vinylpolypyrolidone) waswashed with THF. The solvent was partly removed by rotary evaporationand residue was precipitated in pentane. After 12 hours at 4° C., thepentane was carefully decanted, leaving the precipitated product. Theresidual solvent was removed by rotary evaporation (40° C./20 mm Hg).The resulting pale yellow viscous liquid was dried (40° C./0.01 mbar) toconstant weight. The product (overall yield 91%) was analyzed by ¹H and¹⁹F NMR. The decanted pentane was also evaporated and returned a lowyield (7%) of a low molecular weight fraction of desired polymer.

Example 1

The UV curing of diacrylated fluoropolymer FP1 to form crosslinkedfluoropolymer networks was carried out using a “UV—system”, availablefrom Applied Curing Technology Ltd., UK. Conditions employed were Speedof conveyor 10 cm/min; UV lamps H and D; lamp distance from theconveyor=10 cm; λ=220-320 nm; parabolic beam, beam density ρ=240 W/cm²;1 pass=2.2 seconds (sec.).

Curable compositions containing FP1 and photoinitiator were made bymixing the diacrylated fluoropolymer and photoinitiator in bulk. Filmsof varying thickness were made for testing by casting the mixture of FP1and photoinitiator to be tested onto aluminum pans. Formulations, filmthickness, curing conditions and a visual estimate of the degree ofcrosslinking in the resulting films are shown in Table I. The terms“good”, “fair”, and “poor” refer to very well crosslinked, suitablycrosslinked and poorly crosslinked, respectively. Non-crosslinked filmsare completely soluble in octane whereas highly crosslinked films arenot. The degree of crosslinking in films treated with UV radiation wasdetermined by estimating the solubility of treated films in octane at25° C. after 16 hours stirring. Films that were completely soluble weredesignated as poor crosslinking, partially soluble films as faircrosslinking and insoluble films as good crosslinking in Table I.

TABLE I Amount Photo- Film Photo- Initiator Thickness Number of Degreeof Sample # Initiator (wt. %¹) (mm) UV Lamp Passes Crosslinking 1Darocur ® 2 0.25 H 2 Good 1173 2 Darocur ® 1 0.25 H 2 Fair 1173 3Darocur ® 3 0.25 H 2 Good 1173 4 Darocur ® 3 0.75 H 2 Poor 1173 5Darocur ® 3 1.5 H 2 Poor 1173 6 Irgacure ® 2 0.25 H 1 Good 819 7Irgacure ® 2 0.75 H 1 Fair 819 8 Irgacure ® 2 1.5 D 2 Fair 819 9Irgacure ® 2 0.25 D 1 Good 907 10 Irgacure ® 2 0.75 D 1 Fair 907 11Irgacure ® 2 1.5 D 2 Fair 907 12 Darocur ® 1.5 0.25 H 2 Fair 1173¹weight percent photoinitiator, based on weight of FP1

Example 2

The UV curing of diacrylated fluoropolymer FP2 to form crosslinkedfluoropolymer networks was carried out using an F 300S/F 300SQ UVmachine (Fusion UV System Inc., USA). Conditions employed were: UV rangeof 200-600 nm and power of 700 W, equipped with conveyor belt (1pass=1.1 sec.).

Curable compositions containing FP2 and photoinitiator were made bymixing the diacrylated fluoropolymer and photoinitiator in bulk. Filmsof varying thickness were made for testing by casting the mixture of FP2and photoinitiator to be tested onto aluminum pans. Formulations, filmthickness, curing conditions and a visual estimate of the degree ofcrosslinking (same test as employed in Example 1) in the resulting filmsare shown in Table II. Also contained in Table II are data on theswelling (percent weight change) of crosslinked films in octane. Theswelling test method employed was to immerse a crosslinked film sampleof 1 cm² surface area and 2 mm thickness into 10 ml of octane. Filmswere immersed at the temperatures indicated and for the times specifiedin Table II. Percent weight (wt.) change was defined as 100(m1−m2)/m2where m1 and m2 refer to the wt. of the swollen sample and the wt. ofthe dry sample, respectively.

TABLE II Swelling in Swelling in Amount Octane, % Boiling Photo- Filmwt. change, Octane, % Initiator Thickness Number Degree of 25° C., 48wt. change, Sample # Photo-Initiator (wt. %²) (mm) of PassesCrosslinking hours 48 hours 13 Darocur ® 2 0.25 15 Good 0 90 1173 14Irgacure ® 819 2 0.25 35 Good −2.1 −8.4 15 Irgacure ® 819 2 0.75 40 Good−2.3 — 16 Irgacure ® 819 2 1.5 40 Good −2.8 −14.6 17 Irgacure ® 2 0.2523 Good −3.2 −20.4 819/DVE-3⁴, 1/1 (wt.) 18 Irgacure ® 2 0.75 23 Good−3.8 — 819/DVE-3⁴, 1/1 (wt.) 19 Irgacure ® 2 1.5 23 Good −4.2 −25.5819/DVE-3³, 1/1 (wt.) ²weight percent photoinitiator, based on weight ofFP2 ³tri(ethylene glycol)divinyl ether

1. A process for the manufacture of a crosslinked fluoropolymer network,said process comprising: A) providing a telechelic diacrylate copolymerof formula CH₂═CR′COO—(CH₂)_(n)—R—(CH₂)_(n)—OOCCR′═CH₂, wherein R′ is Hor —CH₃, n is 2 or 3 and R is an oligomer having a number averagemolecular weight of 1000 to 25,000 daltons, said oligomer selected fromthe group consisting of i) an oligomer comprising copolymerized units ofvinylidene fluoride and perfluoro(methyl vinyl ether), ii) an oligomercomprising copolymerized units of vinylidene fluoride andhexafluoropropylene, iii) an oligomer comprising copolymerized units oftetrafluoroethylene and perfluoro(methyl vinyl ether), and iv) anoligomer comprising copolymerized units of tetrafluoroethylene and ahydrocarbon olefin; B) mixing said diacrylate copolymer with a source offree radicals selected from the group consisting of photoinitiators andorganic peroxides to form a curable composition; and C) generating freeradicals to form a crosslinked fluoropolymer network.
 2. A process ofclaim 1 wherein said oligomer has a number average molecular weight of1200 to 12,000 daltons.
 3. A process of claim 2 wherein said oligomerhas a number average molecular weight of 1500 to 5000 daltons.
 4. Aprocess of claim 1 wherein said oligomer comprises copolymerized unitsselected from the group consisting of i) vinylidene fluoride,tetrafluoroethylene and perfluoro(methyl vinyl ether); ii)tetrafluoroethylene, perfluoro(methyl vinyl ether) and ethylene; iii)vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene; andiv) tetrafluoroethylene, vinylidene fluoride and propylene.
 5. A processof claim 1 wherein said source of free radicals is a photoinitiator andfree radicals are generated by exposing said curable composition to UVlight.